Comparison between NIRS and fMRI

I have a friend who has been using fMRI for more than 10 years and now a professor. He heard NIRS might be a good technology to measure human brain but knew little about it. So what is the difference between NIRS and fMRI? This is probably a common question for fMRI researchers who are looking for alternative ways to do brain imaging.

So here is some side-by-side comparison between NIRS and fMRI:

	NIRS	fMRI	Note
Measurement	both oxy- and deoxy-Hb	BOLD signal	That means you get two number per location at a time in NIRS
Temporal resolution	10Hz	0.5Hz	In fMRI TR is usually 2s
Spatial resolution	30mm	2-4mm
Measurable region	Only surface	Entire brain
Real-time application	easy	difficult
Real-life application	easy	difficult	such as exercise, natural conversation etc
Hyperscanning application	easy	difficult
Cost	Cheaper $100-500K	Expensive >$2M	NIRS price largely depends on the number of channels
Maintenance Cost	Cheap	Expensive	NIRS has ~0 maintenance cost; fMRI usually requires a on-site expert
Portability	Can be	No	There are some portable NIRS devices available
Signal to noise ratio	lower	higher
Subjects with Dental Braces and Retainers, or ear rings	Safe	might not be safe
Subjects with Pacemaker or metals in brain	Safe	unsafe